Singer 404 -- The workhorse straight-stitcher so tough that even junior high school home ec students can't kill one, right? That's what I thought when I bought it. But I could not get that machine to free up the least little bit. 6 months later, she moves. What was it? Copious quantity of lint left in the bobbin case (lint, not thread) had absorbed moisture and rusted the parts together. And the hook was seized in the wrong position so that I could not remove the bobbin case. Could not turn the hand wheel, could not make the bobbin case even rattle in there. Nothing would move. I doused the entire machine with sewing machine oil and then Liquid Wrench, but gave up when it still would not move 3 weeks later. I forgot about it until last weekend, and was pleased to find that after about 6 months the seized parts finally let go. I will have to lightly steel-wool a few areas. I scraped a boatload of oily lint out of there
There is a warning in the Singer 404 manual to clean out the lint so as not to get rust in there, lol. Other Slants might have the same issue.
I found that 404 in a used furniture store. Nice looking 404 in a nice cabinet, with attachments and a slant buttonholer with it. The motor was good, the cabinet was decent, but that machine as jammed up so tight that nothing would move at all.
The store owner made me an offer I could not refuse: $5 for the entire package. Such a deal!
So, if you run across a really siezed-up 404 and the motor still runs, now you know what to do: Act disinterested, furrow your brow, offer $5 ,"because it might have a broken gear or something." LOL